1. Field
This document relates to a light emitting display device and its driving method.
2. Related Art
In general, a light emitting display device is a self-emission type display device that emits light by electrically exciting fluorescent compounds, and with its advantages that it may be driven at a low voltage, may be easily formed to be thin and has a wide viewing angle and fast response speed, the light emitting display device receives much attention as a next-generation display device which may overcome the drawbacks of the liquid crystal display.
An organic light emitting display device comprises an organic luminescence layer between an anode and a cathode in which holes provided from the anode and electrons received from the cathode are combined to form exciton, namely, a pair of hole-electron, and the organic light emitting display device emits light by energy generated as the exciton returns to its bottom state. The organic light emitting display device may comprise a hole (electron) transport layer and/or hole (electron) injection layer between the anode or the cathode and the light emission layer.
The organic light emitting display device may be divided into a passive matrix type organic light emitting display device and an active matrix type organic light emitting display device according to a driving method.
FIG. 1 shows a frame structure of the related art digitally driven organic light emitting display device.
Referring to FIG. 1, one frame of a sub-pixel is divided into six sub-fields, namely, first to six sub-fields (SF1 to SF6), to indicate (display) 6 bits. In this case, respective sub-fields SF1 to SF6 comprise an address period and a display period.
The address period is the same at every sub-field and refers to a period during which a data signal is applied to a sub-pixel selected by a scan signal and stored in a capacitor of the sub-pixel. During the address period, the data signal is stored in the capacitor and also an organic light emitting diode (OLED) is illuminated.
The display period is a period during which illuminating of the OLED is maintained by using the data signal stored in the capacitor Cst until a next data signal is applied. The display period has a binary weight. Namely, illumination periods of the respective sub-fields are SF2=2*SF1, SF3=4*SF1, SF4=8*SF1, SF5=16*SF1, and SF6=32*SF1. Accordingly, the display period lengthens as it goes up to the relatively higher gray levels, and shortens as it goes down to the relatively lower gray levels.
In the organic light emitting display device that comprises the plurality of sub-pixels, in a state that scan signals (scan signals 1, 2, 3, and 4, . . . ) are applied through scan lines to the sub-pixels during the address period, data signals are inputted through the data lines. Then, upon receiving the data signals, the sub-pixels maintain their luminous state during the display period until the next data signal is applied.
As described Referring to FIG. 1, in the case where a single frame comprises six sub-fields and the display period has the binary weight, gray levels of respective sub-pixels are represented according to combinations of display time of the six sub-fields.
However, in the related art organic light emitting display device, a minimum display time corresponds to duration from when a first scan signal is inputted to when a final scan signal is inputted, so minimum luminance increases. In particular, in case of the organic light emitting display device with high resolution, an increase in the number of scan lines leads to an increase in the minimum display time, which results in an increase in the minimum luminance.